Identification Of Antagonist Against Anthracnose Of Papaya Fruit And Study On Its Antimicrobial Ingredient And Mechanism Of Action

Papaya(Carica papaya L.) is one of the tropical and subtropical fruits that has great development potential. However, papaya is perishable and highly susceptible to postharvest microbial decay during storage and transportation, leading to economic losses. Anthracnose caused by Collet otrichum gloeosporioides Penz. is a major postharvest disease of papaya fruit. Biological control was regarded as a control method which is safe for human and environment, correspondingly, there are less study on the biological control of anthracnose of papaya fruit in China, and effective antagonistic bacteria resources are less, which limited the development of biological control technology against the postharvest disease of fruits and vegetables. In this study, antagonistic bacteria with good control effect on anthracnose of papaya was isolated and purified from the pericarp of papaya fruit, then the strain was identified and its antimicrobial substance and mechanism of action was investigated. The results are as follows:1、451strains was isolated and purified from the pericarp of papaya fruit. After primary and secondary screening,20strains showed good antagonistic effects on plate. Among them,1w320strain was screened out with strong inhibitory effect on papaya anthracnose. Confront culture tests showed that strain lw320had strong antifungal activity to14kinds of pathogenic fungus. The antagonistic index all are above1.42and the highest reached2.90. According to morphological, biophysiological and biochenmical characteristics and16S rDNA sequence homo logy, the strain was identified as Bacillus amyloliquefaciem. In the postharvest disease control experiment, the strain lw320showed76.5%control effect on Collet otrichum gloeosporioides of postharvest papaya fruit.2、The tests by using oxford cup method in vitro showed that the fermentation filtrate of strain1w320had strong control effect on C. gloeosporioides with the inhibition zone diameter of about20mm. What’s more, volatile metabolites and non-volatile metabolites from them inhibited mycelia growth of C. gloeosporioides significantly. Research on the physical and chemical properties of fermentation supernatant showed that the antimicrobial substance is not sensitive to temperature, pH, proteinase K and common mental ions. Which indicated it has a potential application in biological control of food and vegetables. After GC-MS analysis, there were10different components in volatiles substances. These components belong to alkane, phenolic, acids, esters and several other unknown components. 3、The antagonistic experiment in vitro showed that the color of mycelia around the inhibition zone deepen to black. The antifimgal substance not only inhibited the hyphal growth, but also caused a series of marked morphological and cell structural alterations including deformation, constriction, sunken and breaking of cell wall, the contents of hyphae exuded. The spores peak was abnormally swollen, with the cell wall disrupted and the cytoplasm leaked. The inoculation test illustrated that lw320strain could also increase the activities of some defense enzymes, such as POD and PPO. All these may inhibit the development of anthracnose of postharvest papaya fruit. Study also showed that the strain1w320had a good effect on preservation of papaya in many aspects, such as postponing the seedcase to turn yellow, delaying flesh softening and changes in soluble solids content.